There are several patent disclosures having keys with a lock and an unlock indicator. See for example U.S. Pat. Nos. 5,870,917; 4,432,218; 4,936,896; 5,548,984 and 6,354,122.
There is a need for a key with a simple lock-unlock indicator such that persons can visually confirm that the operator has locked a complementary lock set by simply viewing the base of the key. Additionally, an audible indicator announcing a lock or unlock condition is sometimes useful.